Attaining Ultraprecision Machining by Feed Drive System Stability Control with Piezoelectric Preloading Actuators

In this paper, a variable preload force control structure utilizing piezoelectric actuators (PEAs) is proposed for the stability control of the feed drive system. Three PEAs are installed between the two nuts to exert preload force on the ball screw, leading to an elimination or substantial reduction of the backlash, which is the main cause of instability of feed drives. This results in better machining precision throughout the operation process. In addition, the force analysis of the whole preload feed drive system is established. Moreover, the hysteresis of the PEAs is determined with reference to the Prandtl–Ishlinskii (P-I) model. Lastly, the P-I model-based feedforward controller is applied to the feed drive system to improve the resultant machining precision. Based on the modeling and experiments, to demonstrate the efficacy and high-performance of the proposed P-I model-based control algorithm against conventional PID control system, comparative experiments are conducted, showing satisfactory results.

A corner smoothing algorithm using Trajectory Pattern Method (TPM) for high-speed and high-quality machining

In micro-line segments machining, transition curves with high harmonic components are more prone to causing vibration issues in the feed drive system, which affects machining efficiency and quality severely. To construct low harmonic trajectories, this paper proposes a corner smoothing algorithm that uses the Trajectory Pattern Method (TPM). The transition curve construction and axial motion scheduling are performed with a specified fundamental frequency in one step, which reduces the smoothing process time and avoids excitation of natural modes of vibration of the system. The synthesized trajectories and axial kinematic profiles are all smooth and only contain the selected fundamental frequency and its first two odd harmonics, which minimizes the number of high harmonic components in the required actuation forces/torques and avoids excitation of the system modes of vibration. Linear programming is used to synthesize the trajectories. The proposed algorithm is shown to achieve near time-optimal trajectories. The provided experimental analysis and comparisons demonstrate that the proposed algorithm achieves smooth axial kinematic profiles with low harmonic contents, which would improve machining efficiency and quality.

Time Domain Simulation of Dynamic Corner Milling Process Considering Chatter Vibration With Finite Amplitude

A number of analysis methods for the process with chatter vibration have been proposed so far. These methods can be used to improve processes stability resulting in better production efficiency. However, the poor estimation accuracy of the phenomenon severely limits the performance of process optimization using the simulation-assisted approach. One of the causes of accuracy deterioration is the modeling error of the phenomenon accompanied by chatter vibration with finite amplitude. In this study, we developed a model that can consider the non-linear uncut chip thickness fluctuation caused by the influence of finite amplitude and the process damping due to the contact of the tool flank face against the finished workpiece surface. Furthermore, we developed a time domain simulator that implements the proposed model, and estimated the finished surface profile of the workpiece based on the results of the time domain simulation. To verify the proposed method, corner machining experiments with an end mill were conducted. Corner machining is frequently used in industrial, but it is known that chatter vibration is likely to occur. In corner machining, machine tools generate motions that accompany acceleration and deceleration. The motion of this feed drive system strongly depends on the dynamic characteristics of the machine tool and the trajectory generation algorithm, which greatly affects the emersion angle of the cutter. Therefore, we simulated the dynamic corner machining process considering the measured data of the motion trajectory of the feed drive system. The estimation result of chatter vibration in corner machining is in good agreement with the measurement result of the machining process. In addition, high-precision estimation of the machined surface profile with chatter mark has been realized.

Dynamics modeling and analysis of feed drive system for a frame saw machine considering time-varying load

Frame saw machine is one of machine tools that is used to process dimension stone. The velocity fluctuation of traditional feed drive system (FDS) lead to excessive wear of diamond particles. The dynamic performance of the FDS has time-varying characteristics during the processing of stone with a large material removal rate. In this paper, a novel FDS was proposed. Firstly, the dynamic modeling of FDS was set up on account of lumped parameter method (LPM). Then the speed of the new FDS was compared with that of the traditional FDS. Finally, the frequency response characteristics of the system were solved by Lagrange and state space method. Results showed that the new FDS has a faster response feed and less velocity fluctuation. The natural frequency and the amplitude of acceleration increase with decreasing load. With the time-varying load, the range of the second-order natural frequency increased by 50 Hz, which was larger than that of the first-order. The modal test verified that the first two natural frequencies of the saw blade are within the range of the natural frequencies of FDS. The proposed FDS can guide for design, reduce the wear of diamond, and improve processing quality.

MODELING AND IDENTIFICATION OF BALL SCREW FEED DRIVE SYSTEMS

In this paper, the ball screw feed drive system is simulated and it?s frequency response is studied. Various parameters effect on the dynamic behavior of the ball screw system have been investigated. Ball screw feed drive system is used in high speed machine tools due to their high efficiency. Estimation of the dynamic behavior of ball screw feed drive mechanism is very important in the industrial processes in order to get high demand for precision and accuracy in machine tools. Optimizing the drive operation can provide significant cost savings. A four degree of freedom system, lumped parameter model is used for modeling a single axis ball screw feed drive system and use it to study and analyze vibrations in this model. The mathematical modeling provides an important information about frequency response when applying different levels of table mass, stiffness of the nut, axial stiffness of the ball screw shaft and torsional stiffness of the ball screw on the system, to describe the effects of these parameters on the system dynamic behavior. The study of dynamic response of ball screw feed drive system provides a better performance control and better understanding of ball screw dynamics.

Transcriptional Characteristics of Quadrant Glitches on Machined Surface – Influence of Tool Diameter and Feed Rate –

When a three-dimensional shape is machined by NC machine tool, motion errors occur around the motion direction changing points of the translational axis. This has a significant influence on a quality of machined surfaces. Therefore, much research on the influence of motion errors around the motion direction changing points of the feed drive system on a machined surface has been conducted to improve the quality of machined surfaces by NC machine tool. Among the motion errors that occur around the motion direction changing points of the translational axis, quadrant glitches with a stick-slip motion have a particularly large influence on the machined surface, and research on compensation methods continues to be reported. However, the transcriptional characteristics of quadrant glitches of the translational axis for machine tools have not been investigated adequately. In this study, the transcriptional characteristics of quadrant glitches of the translational axis on a machined surface were investigated. In addition, the influences of various factors on the transcriptional characteristics of quadrant glitches on a machined surface were investigated using a proposed equation and actual machining tests.